Case Studies: Drainage Water Phosphorus Losses in the Great Lakes Basin.

The great lakes are one of the most important fresh water resources on the planet. While forestry is a primary land use throughout much of the great lakes basin, there are portions of the basin, such as much of the land that drains directly to Lake Erie, that are primarily agricultural. The primary agricultural soils in the great lakes basin are primarily glacially derived, although a large portion of the western Lake Erie basin is derived from lake plain soils, which tend to have much worse internal drainage and also tend to be flatter than the glacially derived soils. Thus require subsurface drainage with supplemental surface drainage. Conservation efforts over the last 25 years have focused on adoption of no-till. These efforts have reduced erosion, as demonstrated by decreases in suspended sediment and total P loadings in the Maumee River; however, soluble phosphorus loadings have increased in the last 15 years. Surface applications of phosphorus, the solubility of phosphorus fertilizers, the limited window for phosphorus fertilizer applications in a corn-soybean rotation, and application of fertilizers once during a two year rotation are the primary culprits in the increased soluble phosphorus loadings. Understanding the sources and mechanisms of phosphorus losses in the great lakes basin is an important first step in limiting the amount of phosphorus loading to the lakes. With this information, this team is developing and testing conservation practices to decrease phosphorus loadings to this sensitive freshwater ecosystem.